Further data on cerebral glucose metabolism in patients made briefly hypothyroid for follow-up examination of thyroid carcinoma, including paired studies before and after stopping thyroid hormone replacement, showed no difference between the euthyroid and hypothyroid state. The study was performed by positron emission tomography (PET scanning) after administration of (F18)deoxyglucose. Lithium ion has the unique property of slowing release of thyroid iodine without impairing iodine uptake and thus may be useful in enhancing the therapeutic effect of I131 on thyroid cancer. Seven patients with metastatic cancer were studied. The rate of release of I131 from 12 tumors in neck, lung or bone was measured before and after lithium. The observed t1/2 was prolonged by lithium in 10 tumors (range 20 to 770%, median 52%) and the effective t1/2, which is proportional to the tumor radiation dose, was increased 30% (from 3.3 plus/minus .4 days to 4.3 plus/minus .4 days). Predicted whole body radiation after lithium ranged from -67% to +89% of the pre-lithium value (mean -3.2%). In 2 patients, an unanticipated increase in whole body radiation, due to tumor destruction with increased I131 release, resulted in significant but transient bone marrow depression. In the preoperative management of thyroid nodules, a one-week trial of prednisone therapy (40 mg per day) was given to evaluate any possible effect in nodule size and any possible correlation in response with the presence of lymphocytic thyroiditis. Ninety-nine patients were studied, and nodule shrinkage greater than 50% in calculated volume was observed in 19%. Further shrinkage occurred in 70% of these when patients were continued on thyroxine therapy and 6 nodules disappeared. Response to prednisone correlated with cytologic evidence of lymphocytic thyroiditis by fine needle aspiration, and with positive antithyroid antibodies in serum.